Field of the Invention
The present invention relates to a holder for a fluid product and method for producing such a holder.
More specifically, the invention relates to a holder that is produced by blow moulding and which has an upright edge with respect to the wall of the holder, for example to act as a base for the holder.
Description of the Related Art
Such a holder can be intended for a large number of different products. In particular, it concerns a beer keg here.
Such a holder can be made in a known way by blow moulding. A preform is hereby made by extrusion, for example. This is a shell of thermoplastic material, for example polyethylene, closed at one end that is at a temperature at which the material is plastic.
This preform is blown against a cooled mould by means of compressed air, whereby an intermediate form occurs, that approximately has the shape and size of the final holder, but is not yet provided with a number of details.
Practically immediately thereafter, if the material is still plastic, a part of the mould, at the location of the position that will become the underside of the holder, is moved with respect to another part of the mould.
As a result the material of the intermediate form is pushed inwards, such that this part of the intermediate form deforms into the final desired shape of the holder.
The parts of the mould are hereby of such a shape that in the end position of the two parts there is a space between the two parts, in which space the edge is formed.
Such producing is generally done in an upside-down orientation, i.e. the underside of the final holder is formed from the top of the preform and intermediate form, at the top of the device in which the holder is produced.
Such traditional producing methods and/or the products thereof are described in for instance DE 1130151 B1, EP 704379 A2, DE 10 2005 001649 A1 and EP 0936149 A1. schobel
When moving the parts of the mould with respect to one another, a significant quantity of material of the wall of the intermediate form is pushed inwards. This material accumulates as a ring-shaped thickening, with an approximately teardrop-shaped cross-section, on the inside of the wall close to the transition between the edge and the wall.
Hereby a constriction can also arise just next to this thickening.
A disadvantage of the holders formed in this way is that a weak spot occurs at the location of the transition between the edge and the wall of the holder, such that tears can occur in the holder during subsequent use.
It is not entirely clear how this weak spot occurs, but the following factors could play a role:                There is a sharp transition between the thickening and the wall, which acts as a stress concentrator;        A constriction, if it occurs, is of course thinner and thus weaker;        As a result of the flow, the polymer chains of the thermoplastic material can take on a preferred direction locally that does not correspond to the direction in which the holder is loaded during use;        In the thickening the cooling of the thermoplastic material is much slower than in the wall, such that internal stresses can occur in the material;        Because the holders are produced upside down so to speak, gravity is largely in the same direction as the flow direction of the thermoplastic material, such that the effects mentioned above occur to a greater extent.        